Although the invention described and claimed herein is primarily directed to individual blade control of a rotor of rotary wing aircraft, it also finds application for use with propellers in a prop-fan configuration.
A review of the evolution of helicopter main rotor design reveals that, while there have been marked changes in the design of the rotor blades and their interconnection to the rotor hub, little has been accomplished to achieve blade feathering (pitch) control. The conventional rotor blade feathering or pitch control still utilizes the complex mechanical swashplate to provide the interface between rotating and non-rotating segments of the system. While progress in the area of helicopter main rotor flight controls has been practically non-existent, there have been many good reasons for this lack of progress. It has been only in the last few years that computer technology is available for such control situations and that fiber optics have been developed to assume certain fly-by-wire tasks heretofore accomplished only by sliding metal slip rings. It is only as the result of recent technological breakthroughs and advancements in many areas that enables reconsideration of the design of main rotor flight control and the radical departure from familiar control arrangements.
Heretofore, in the case of helicopter rotors, both cyclic and collective pitch is achieved by use of a swashplate in connection with hydraulic actuators which are mechanically controlled. Helicopters are generally equipped with mechanical linkages leading from pilot control sticks to the hydraulic actuator inputs to control the location and attitude of the swashplate. The swashplate is coupled to pitch horns on the rotor blades to control both cyclic and collective pitch. Variations in cyclic pitch are produced by tilting the swashplate and variations in collective pitch are produced by raising and lowering the swashplate. The position and attitude of the swashplate are usually controlled by three hydraulic actuators connected to three points on the swashplate. Although historically, mechanical linkages interconnect the pilot control sticks to the actuators, recent developments have incorporated the use of electrical sensors to sense pilot inputs for producing control signals for servo systems, which, in turn, drive electrohydraulic actuators coupled to the swashplate.
The swashplate and associated linkages, in addition to the actuators, require a considerable amount of space in the aircraft and account for a substantial amount of additional aircraft gross weight. In the case of military aircraft, the extensive mechanical linkages and mechanisms for controlling the swashplate, in cyclic and collective pitch, increase the danger of damage by enemy fire. Thus, there is a continuing effort to improve blade pitch control for helicopter rotors and for propellers in a prop-fan configuration.
In accordance with the present invention, the conventional complex mechanical swashplate is eliminated from the main rotor flight controls thereby providing the potential for improvements in reliability and maintainability. The apparatus described herein provides a two-fail-operate system that integrates actuators, power supplies and control logic into the rotating system. Individual blade control is most effective in terms of reduction in both linkage and power required with any apparatus of the present invention.